Crossbar interconnect technology has been developed in recent years with a primary focus in applications in information storage and retrieval. A crossbar array basically comprises a first set of conductive or semiconductive parallel wires and a second set of conductive or semiconductive parallel wires formed so as to intersect the first set of wires. The intersections between the two sets of wires are separated by a thin film material or molecular component. A property of the material, such as the material resistance, may be altered by controlling the voltages applied between individual wires from the first and second set of wires. Alteration of the materials resistance at an intersection may be performed so as to achieve a high resistance or low resistance state and thus store digital data. It is noted that crossbar arrays are occasionally referred to as crosspoint or crosswire arrays.
Nagasubramanian et al. U.S. Pat. No. 5,272,359 discloses such a crossbar array employing a TCNQ doped organic conducting polymer as the material. Resistance variation from 1012 ohms to 107 ohms is reported to be achieved by applying a 10V pulse with a 100 ms duration. Nagasubramanian et al. discusses the uses of the crossbar array as forming a memory matrix for an artificial neural net.
Other materials useful for electrically programmable resistance are those with a perovskite structure such as magnetoresistive materials (U.S. Pat. Nos. 6,531,371 and 6,693,821), a variety of organic semiconductors (U.S. Pat. Nos. 6,746,971 and 6,960,783), and silver-selenide/chalcogenide laminate films (U.S. Pat. No. 6,867,996).
Kuekes et al. U.S. Pat. No. 6,128,214 uses crossbars applicable at nanometer scales by employing molecular components as a bridging component between the wires. Such nanoscale crossbars have been disclosed as useful tools in molecular electronics capable of performing a variety of tasks including signal routing, multiplexing, and performing simple logic functions in U.S. Pat. Nos. 6,256,767, 6,314,019, 6,518,156, 6,586,965, 6,812,117, 6,854,092, 6,858,162, 6,870,394, 6,880,146, 6,898,098, 6,900,479, 6,919,740, 6,963,077, and 7,203,789. Molecular crossbar arrays used in neural networks is disclosed in U.S. Pat. No. 7,359,888. Manufacturing of molecular crossbar arrays is taught in U.S. Pat. Nos. 6,248,674, 6,432,740, 6,835,575, 6,846,682, and 6,998,333.
Examples of non-patent literature concerned with molecular crossbar arrays include Ziegler et al. “A Case for CMOS/nano Co-design,” Lee et al. “CMOL Crossnets as Pattern Classifiers,” and Das et al. “Architectures and Simulations for Nanoprocessor Systems Integrated On the Molecular Scale.” Reinhold Koch provides a discussion of programmable crossbar arrays formed from ferroelectric material in Scientific American Vol. 293, No. 2 pgs. 56-63.
In the parent U.S. patent application Ser. No. 11/798,647 and U.S. Pat. No. 7,302,513, which are incorporated by reference in their entirety, a variety of different configurations of crossbar arrays are taught. In order to easily reprogram the states of the crossbar array symmetrical crossbar architectures are preferable so that reversal of a programmed impedance or resistance state is achievable without complex programming circuitry. Furthermore, the crossbar architectures should be designed to avoid or minimize feedback paths and electrical crosstalk within the crossbar array. The present patent application focuses on configurations to achieve these ends.